Mobile screening apparatus and method

ABSTRACT

A mobile screening apparatus includes a wheel-supported main frame and a hopper mounted at or near to one end of the main frame. An elevator mounted on the frame feeds material received from the hopper to a screening device which screens the material into different size ranges. Discharge conveyors discharge different size ranges of the screened material to respective discharge positions. A tractor unit is releasably coupled with a towing coupling provided at one end of the main frame. The tractor unit is operative to move the apparatus over the ground while screening operations take place so that traveling deposits of screened material can be formed. A power plant mounted on the frame is arranged to drive the screening device, the elevator, and the discharge conveyors.

This invention relates to a mobile screening apparatus, and to a methodof screening material and depositing the screened material while theapparatus is moving over the ground.

Screening apparatus are used to screen crushed rock, and other supply ofparticulate raw material into different size ranges of screenedparticles, and to distribute the screened fractions to separatedischarge positions.

In a typical installation of a screening apparatus or plant in a quarry,the apparatus has a number of separate discharge conveyors or elevators,each being associated with a separate screening fraction from the usualmulti-deck screen, and which can deposit separate stockpiles ofdifferent sizes e.g. sand, small aggregate or gravel, and ballastsuitable for building or road foundation work.

At some sites, a screening plant is set-up as a permanent, orsemi-permanent installation, and which is assembled on site, and whichhas to be dis-assembled and transported as separate components beforere-assembly at a new site. However, at other locations, it is known anddesirable to use mobile screening apparatus which can be towed from onesite to another, and including along the public highway. Mobileapparatus can be converted relatively easily between a transport modeand an operative screening mode.

The present invention is concerned with what is believed to be a uniqueconcept in screening apparatus, in that it enables, when desired,screening operations to be carried out while the apparatus is movingover the ground.

According to one aspect of the invention there is provided a mobilescreening apparatus which comprises:

a wheel-supported main frame;

a hopper mounted at or near to one end of the main frame to receive asupply of bulk material which is to be screened;

an elevator mounted on the frame and having a lower receiving endarranged to receive material from the hopper, and to convey thismaterial to an upper discharge end of the elevator;

a screening device mounted on the frame and arranged to receive materialfrom the discharge end of the elevator, and to screen the material intodifferent size ranges;

discharge means associated with the screening device and operative todischarge the different size ranges to respective discharge positions;

a towing coupling provided at said one end of the frame; and

a tractor unit releasably coupled with said towing coupling andoperative to move the apparatus over the ground while screeningoperations take place, whereby travelling deposits of screened materialcan be formed.

The tractor unit may be used to tow the apparatus at a continuousrelatively slow speed, or to move the apparatus in small increments,according to the requirements for the travelling deposit of screenedmaterial.

According to a further aspect of the invention there is provided amobile screening apparatus which comprises:

a wheel-supported main frame;

a hopper mounted at or near to one end of the main frame to receive asupply of bulk material which is to be screened;

conveyor means mounted on the main frame and having one end arranged toreceive material from the hopper, and an opposite end forming adischarge end;

a screening device mounted on the frame and arranged to receive materialfrom the discharge end of the conveyor means, and to screen the materialinto different size ranges;

discharge means associated with the screening device and operative todischarge the different size ranges to respective discharge positions;

a towing coupling provided at said one end of the frame;

a power plant arranged to drive the screening device, the conveyingmeans, and the discharge means; and

a tractor unit releasably coupled with said towing coupling, saidtractor unit being arranged to derive its motive power from said powerplant in order to move the apparatus over the ground when required.

Preferably, the power plant is mounted on the main frame of thescreening apparatus, and any suitable means may be used to transmitmotive power to the tractor unit. By way of example only, the tractorunit may have a hydraulic drive motor, and the power to operate themotor may therefore comprise hydraulic pressure flow and return linesrunning between the power plant and the hydraulic motor, and withreleasable couplings provided in the pressure lines to permit thetractor unit to be uncoupled from the screening apparatus e.g. when theapparatus is required to carry out screening operations at a particularfixed location.

In both aspects of the invention, the tractor unit is preferablyprovided with endless or crawler tracks, and will normally move atrelatively slow speed. The tractor unit may have a driver's cab, if itis desired to provide driver control of the movement and operation ofthe screening apparatus.

However, it is within the scope of the invention for the tractorunit/screening apparatus combination to be operated by remote control,if required, e.g. by use of radio or infrared remote control.

Preferably, the screening apparatus has a number of separate dischargeconveyors, corresponding in number to the number of different sizeranges of screened material derivable from the screening device, and atleast some of the conveyors may be arranged to be convertible betweeninoperative stowed positions e.g. suitable for transport when it isrequired to move the apparatus from one site to another, (and of minimumprojection from the general body of the apparatus), and extendedoperative positions for discharge of screened material some distanceaway from the general body of the apparatus.

The apparatus may have one or more "side conveyor", which can projectlaterally of the apparatus, and which can form a travelling heap ofdeposited screened material alongside the apparatus while the latter ison the move. Alternatively, the side conveyor may cause progressivefilling of trenches alongside the travelling apparatus e.g. forback-filling of pipelines laid in the trenches.

The apparatus may also have a so-called "tail conveyor", which projectsrearwardly of the apparatus in a discharge position, and which can allowa trailing heap of deposited material to be formed which follows thetravelling apparatus. Alternatively, the tail conveyor may be omitted,and the screening device may be arranged to discharge at least part ofthe screened fraction of material directly to the ground as a trailingdeposit of material.

The travelling screening apparatus therefore can form continuous orintermittent travelling deposits of screened material e.g. travellingheaps of deposited material alongside and/or trailing behind theapparatus, somewhat in the manner of harvested crops deposited in afield by a harvesting machine in the form of "windrows".

The screening device may take any suitable form, and may comprise amulti-deck screen, a single screen, bar grizzly type screen, or anyother screening elements known per se for use in screening crushed rockand other minerals, or even bulk raw material supplied during siteexcavation, which can include soil, building rubble, tree roots etc.

The towing coupling can take any suitable form to allow easy coupling,and uncoupling between the screening apparatus and the tractor unit. Ina preferred arrangement, the towing coupling is provided on theunderside of a base or platform on which the hopper is mounted, and thetowing coupling may comprise a "fifth wheel coupling" known per se.However, other types of towing coupling may be used including a slewring type of coupling.

The invention also includes a method of screening material anddepositing the screened material, utilising a mobile screening apparatusaccording to said one or to said further aspect of the invention, andoptionally with preferred features thereof referred to above.

A preferred embodiment of mobile screening apparatus according to theinvention will now be described in detail, by way of example only, withreference to the accompanying drawings, in which:

FIG. 1 is a side view of a mobile screening apparatus according to theinvention and forming part of a towed combination with a tractor unit;and

FIG. 2 is a front view of the combination, and with side conveyorsunfolded to operative discharge positions for discharging respectivescreened fractions of material from a screening device of the apparatus.

Referring now to the drawings, a mobile screening apparatus according tothe invention is designated generally by reference 10, and comprisesscreening plant 11 and tractor unit 12 forming a towed combination.However, plant 11 can operate as a "stand alone" installation in orderto carry out screening functions as required.

The screening plant 11 comprises a wheel-supported main frame or chassis13 having a tandem axle wheelset 14 supporting the rear end of thechassis, and provided with a hopper 15 mounted at or near to the frontend of the chassis 13. Hopper 15 can be of conventional construction,and is arranged to receive a supply of bulk material which is to bescreened.

A conveying means is mounted on chassis 13 to convey material from thehopper 15 to a screening device 16, and comprises an elevator 17 havinga lower receiving end 18 arranged to receive material from the hopper15, and an upper discharge end 19 from which the elevated material isdischarged to the screening device 16. The screening device 16preferably comprises a screen box comprising a multi-deck arrangement ofscreens, and which is pivotally mounted on the chassis 13 for adjustmentpurposes, to co-operate automatically with length wise adjustment of theelevator 17, in a preferred arrangement, which is disclosed in moredetail in European Patent No 0301798.

The screening device 16 screens the material into different size rangesin any suitable well-known manner and discharge means is associated withthe screening device 16 and is operative to discharge the different sizeranges to respective discharge positions. The discharge means, in theillustrated embodiment, comprises a pair of foldable side conveyors 20,which are shown in FIG. 2 in laterally extended discharge positions. Theplant 11 may also be provided with a "tail conveyor" 21, which is shownin FIG. 1 in the rearwardly extended operative position for depositingscreened material in a heap to the rear of the apparatus.

A towing coupling is provided at the forward end of the main frame 13,and tractor unit 12 is releasably coupled with the towing coupling andis operative to move the screening apparatus over the ground whilescreening operations take place whereby travelling deposits of screenedmaterial can be formed. The towing coupling is preferably provided onthe underside of a base or platform 22 of hopper 15 and may comprise acoupling element suitable for making sliding contact with a fifth wheelcoupling 23 which is mounted on a load bearing platform 24 on tractorunit 12 in any well-known manner. However, other types of towingcoupling may be provided including a slew ring arrangement.

A power plant is mounted on chassis 13 and is arranged to drive thescreening device 16, elevator 17 and the discharge conveyors 20 and 21.The power unit is shown by reference 25 in FIG. 1, and comprises a motorand drive trains (not shown in detail) to operate the various componentsof the screening apparatus in any suitable known manner.

The tractor unit 12 may comprise a driver's cab, if it is desired toprovide driver control of the movement and operation of the screeningapparatus. However, if it is required to provide remote control over themovement and operation of the tractor unit/screening apparatuscombination, this may be achieved by use of radio or infra-red remotecontrol. The tractor unit 12 is preferably arranged to derive its motivepower from the power plant 25, and this may be achieved by use of anysuitable power transmission means e.g. using hydraulic pressure flow andreturn lines running between power plant 25 and a hydraulic drive motoror motors in the tractor unit 12.

The tractor unit 12 is primarily intended to be a relatively slow speedmotive unit, and therefore is provided with endless or crawler tracks26.

As mentioned above, screening plant 11 can be operated in a "standalone" mode, but when it is coupled to tractor unit 12, it can bereadily towed to a desired new location, and if it is being moved aconsiderable distance, the screening plant 11 can be converted totransport mode by suitable folding of the discharge conveyors to stowedpositions. However, if it is desired to carry out screening operationswhile the plant is travelling, so as to form travelling deposits ofscreened material, the screening apparatus can be operating continuouslywhile it is being towed, and with the discharge conveyors in thedischarge position. Heaps of screened material can be formed as separatedeposits alongside the travelling apparatus and/or as trailed depositsbehind it, or the material can be discharged to form foundationmaterial, or to fill trenches as back-fill, following laying ofpipelines into the trenches.

What is claimed is:
 1. A mobile screening apparatus which comprises:awheel-supported main frame; a hopper mounted at or near to one end ofthe main frame to receive a supply of bulk material which is to bescreened; an elevator mounted on the frame and having a lower receivingend arranged to receive material from the hopper, and to convey thismaterial to an upper discharge end of the elevator; a screening devicemounted on the frame and arranged to receive material from the dischargeend of the elevator, and to screen the material into different sizeranges; discharge means associated with the screening device andoperative to discharge the different size ranges to respective dischargepositions; a towing coupling provided at said one end of the frame; anda tractor unit releasably coupled with said towing coupling andoperative to move the apparatus over the ground, said tractor unit beingshort in length relative to the length of the screening apparatus andbeing supported by endless tracks so as to render the tractorunit/screening apparatus combination highly maneuverable, the tractorunit including a driver's cab to permit driver control of the movementand/or operation of the screening apparatus.
 2. Apparatus according toclaim 1, in which the tractor unit/screening apparatus combination isarranged to be capable of operation by remote control.
 3. Apparatusaccording to claim 1, in which the discharge means comprises at leastone side conveyor.
 4. Apparatus according to claim 3, including meansfor discharging one fraction of screen material rearwardly of theapparatus.
 5. Apparatus according to claim 1, including a tail conveyormounted at the rear end of the apparatus.
 6. Apparatus according toclaim 1, in which the hopper includes a screening device which isoperable to carry out at least a preliminary screening operation on thebulk material.
 7. A mobile screening apparatus which comprises:awheel-supported main frame; a hopper mounted at or near to one end ofthe main frame to receive a supply of bulk material which is to bescreened; conveyor means mounted on the main frame and having one endarranged to receive material from the hopper, and an opposite endforming a discharge end; a screening device mounted on the frame andarranged to receive material from the discharge end of the conveyormeans, and to screen the material into different size ranges; dischargemeans associated with the screening device and operative to dischargethe different size ranges to respective discharge positions; a towingcoupling provided at said one end of the frame; a power plant arrangedto drive the screening device, the conveying means, and the dischargemeans; and a tractor unit releasibly coupled with said towing coupling,said tractor unit being arranged to derive its motive power from saidpower plant in order to move the apparatus over the ground whenrequired.
 8. Apparatus according to claim 7, in which the power plant ismounted on the main frame of the screening apparatus.
 9. Apparatusaccording to claim 8, in which the tractor unit includes one or morehydraulic drive motors operable by hydraulic pressure flow and returnlines running between the power plant and the one or more hydraulicdrive motors.
 10. A method of screening a supply of bulk material anddischarging the screened bulk material at spaced-apart dischargepositions, the method comprising the steps of:receiving a supply of bulkmaterial within a hopper, the hopper being mounted at or near to one endof a wheel-supported main frame, the one end of the main frame alsobeing releasably coupled with a tractor unit, the tractor unit beingshort in length relative to the length of the main frame and beingsupported by endless tracks; elevating the bulk material from the hopperto an elevated screening device mounted on the main frame; screening thebulk material into different size ranges through the screening device;discharging the screened bulk material to respective dischargepositions; and moving the wheel-supported mainframe via the tractor unitwhen it is required to form further stockpiles, and carrying out furtherscreening operations.
 11. A mobile screening apparatus which comprises:awheel-supported main frame; a hopper mounted at or near to one end ofthe main frame to receive a supply of bulk material which is to bescreened; an elevator mounted on the frame and having a lower receivingend arranged to receive material from the hopper, and to convey thismaterial to an upper discharge end of the elevator; a screening devicemounted on the frame and arranged to receive material from the dischargeend of the elevator, and to screen the material into different sizeranges; discharge means associated with the screening device andoperative to discharge the different size ranges to respective dischargepositions; a towing coupling provided at said one end of the frame; anda tractor unit releasably coupled with said towing coupling andoperative to move the apparatus over the ground, said tractor unit beingshort in length relative to the length of the screening apparatus andbeing supported by endless tracks so as to render the tractorunit/screening apparatus combination highly maneuverable, the tractorunit/screening apparatus combination being arranged so as to be capableof operation by remote control.
 12. A mobile screening apparatus whichcomprises:a wheel-supported main frame having a forward end; a hopperpositioned at the forward end of the main frame, the hopper beingconfigured to receive a supply of bulk material to be screened; asupport platform configured to support the hopper, the support platformbeing secured to the forward end of the main frame; an elevator mountedon the main frame and having a lower receiving end and an upperdischarge end, the lower receiving end being configured to receivematerial from the hopper; a screening device mounted on the main frameand configured to receive material from the discharge end of theelevator and screen the material into different size ranges; meansassociated with the screening device for discharging the different sizeranges of the material to respective discharge positions; a releasablecoupling positioned on the underside of the support platform; and atractor unit releasably coupled with the coupling on the supportplatform and operative to move the apparatus over the ground duringscreening of the material, the tractor unit being supported by endlesstracks which are short in length relative to the length of the screeningapparatus so as to render the tractor unit/screening apparatuscombination maneuverable.
 13. A mobile screening apparatus as recited inclaim 12, further comprising a brace downwardly projecting from theunderside of the support platform, the brace being configured to supportthe releasable coupling off the ground surface when the tractor unit isseparated from the support platform.